The invention relates to a device for inserting and thrusting a square bar into a press piercing mill, the bar being disposed along the rolling and drilling axis of the mill. More specifically, the invention relates to a device for performing the following operations in a fixed sequence:
(a) Positioning a square bar along the rolling and piercing axis of a press piercing mill at its inlet side,
(b) Inserting the bar through the inlet guide of the press piercing mill, and
(c) Inserting and thrusting the bar between the rolls and against the drill bit of the mill.
A press-piercing mill is a machine capable of converting a hot square bar into a round, axially pierced blank. A machine of the aforementioned kind, which hereinafter will be denoted by the abbreviation PPM, substantially comprises a double rolling machine comprising rolls having round grooves, a mandrel bearing a bit and mounted along the rolling and piercing axis of the rolling machine on the outlet side thereof, a drill bit secured to the end of the mandrel facing the rolling machine, and a substantially tunnel inlet guide coaxial with the rolling and piercing axis, for guiding a square bar to the rolling machine.
In order to convert a square bar into a round, axially pierced blank in a PRM, the bar must be held exactly along the rolling axis of the machine and thrust between the grooves in rolls and against the drill bit.
It is known that, in order to meet rolling and piercing requirements in an optimum manner, the axial thrust on the bar must be considerable, whereas the bar is moved between the cylinders and against the drill bit at a relatively low, constant speed, e.g. on average of the order of 0.4 m/sec.
To this end, use has hitherto been made of a high-power hydraulic or mechanical actuator capable of moving a longitudinally-guided slide at low velocity in a direction parallel to the PPM rolling axis, the slide being fitted with a thrust rod having a longitudinal axis coinciding with the rolling axis and adapted to act on the bar.
A slide of the aforementioned kind can be moved, relative to the PPM, from a remote position in which a space for holding a square bar is left between the free end of the thrust rod and the PPM inlet guide inlet, and a position near the inlet of the double rolling machine but not interferring therewith.
The distance travelled by the square bar between the moment when it is positioned between the thrust rod and the PPM inlet guide and the moment in which it is completely converted into a round axially pierced blank can be divided into the following two sections:
1. Insertion of the bar. This is the travel section between the inlet guide mouth and the position in which the front end of the square bar makes contact with the rolls and
2. The thrust section. This is the remaining distance travelled, during which the bar is thrust between the rolls and against the drill bit and is converted in a desired manner into a corresponding round pierced blank.
Sections 1 and 2 of the aforementioned travel both occur at low velocity, i.e. the fixed low velocity of operation of the actuator. Furthermore, in order to position a new square bar along the rolling axis upstream of the inlet guide, it is necessary to wait until the slide, moved at low velocity by the actuator, has reached the position remote from the PPM so as to leave space for receiving a bar between the thrust rod and the PPM inlet guide.
This results in idle time which considerably affects the productivity of the PPM, due to the low speed hitherto adopted for inserting the bar and for the entire return of the slide to the position remote from the PPM, in addition to the thrust section, during which the low speed is imposed by recognized operational and structural requirements of the PPM. Besides the aforementioned idle time, additional time is required for positioning a new square bar in the space between the thrust rod and the inlet guide mouth. Such positioning has hitherto been brought about by conventional, relatively slow lifting and transfer devices.
This hitherto inevitable idle time has been the main technical disadvantage of conventional positioning, insertion and thrust devices for PPM's. The disadvantage is even more clear when the PPM is used to produce round pierced blanks for a downstream pipe rolling mill which operates at the rate of four or more workpieces per minute.
The invention is based on the problem of providing a device having structural and functional features such that it can position a square bar along a PPM rolling axis in line with a PPM inlet guide, insert the bar through the guide and subsequently thrust the bar between the rolls and against the drill bit in a manner which reduces or completely obviates the aforementioned serious technical disadvantage.